带有 customArrayAdapter 的 ArrayList 仅显示 1 个列表

Question

我已经使用 customArrayAdapter 创建了数组列表，并且在使用模拟数据时，列表在屏幕上是可见的，没有任何错误，但是当我用 JsonObject 替换模拟数据时，json 响应被硬编码为字符串值在 java 文件中，然后我发现所有数据都正确显示在列表中，但屏幕中只显示 1 个列表项而不是 15 个，因为响应包含 15 个 JsonArray 对象。我已经使用 for 循环遍历 JsonArray 但我不知道错误是什么？

MainActivity.Java :

package com.example.anybookinfo;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.widget.ListView;

import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ListView bookListView = findViewById(R.id.bookListView);
        ArrayList<BookStore> bookStoreArrayList = HTTTP_REQUEST.readFromJson(HTTTP_REQUEST.jsonResponse);

        BookAdapter bookAdapter = new BookAdapter(this, bookStoreArrayList);

        bookListView.setAdapter(bookAdapter);
    }
}

HTTP_Request.java :

package com.example.anybookinfo;

import android.text.TextUtils;
import android.util.Log;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.util.ArrayList;
public final class HTTTP_REQUEST {
public static ArrayList<BookStore> readFromJson(String jsonObject) {
        ArrayList<BookStore> currentBookStore = new ArrayList<>();
        if (TextUtils.isEmpty(jsonObject)) {
            return null;
        }
        try {
            JSONObject root = new JSONObject(jsonObject);
            JSONArray items = root.getJSONArray("items");
            for (int i = 0; i < items.length(); i++) {
                JSONObject currentBook = items.getJSONObject(i);
                JSONObject volumeInfo = currentBook.getJSONObject("volumeInfo");
                String fTitle = volumeInfo.getString("title");
                String lTitle = volumeInfo.getString("subtitle");
                JSONArray author = volumeInfo.getJSONArray("authors");
                String authorName = author.getString(0);
                int PageCount = volumeInfo.getInt("pageCount");
                JSONObject saleInfo = currentBook.getJSONObject("saleInfo");
                JSONObject listPrice = saleInfo.getJSONObject("listPrice");
                double amount = listPrice.getDouble("amount");
                String currencyCode = listPrice.getString("currencyCode");
                JSONObject searchInfo = currentBook.getJSONObject("searchInfo");
                String textSnippet = searchInfo.getString("textSnippet");
                BookStore bookStore = new BookStore(fTitle, lTitle, authorName, textSnippet, PageCount, amount, currencyCode);
                currentBookStore.add(bookStore);
            }
        } catch (JSONException j) {
            Log.e("readFromJson Error", "error in reading the json response", j);
        }
        return currentBookStore;
    }
 public static final String jsonResponse = "  //the json response code is here " ;
}

硬编码的实际 json 响应 link： https://www.googleapis.com/books/v1/volumes?q=Inner%20Engineering%20:%20a%20yogi%27s%20guide%20to%20joy&maxResults=15

LogCat Error :

01-24 23:18:46.030 3693-3703/? E/art: Failed sending reply to debugger: Broken pipe
01-24 23:18:46.243 3693-3693/? E/readFromJson Error: error in reading the json response
    org.json.JSONException: No value for listPrice
        at org.json.JSONObject.get(JSONObject.java:389)
com.example.anybookinfo.HTTTP_REQUEST.readFromJson(HTTTP_REQUEST.java:58)
        at com.example.anybookinfo.MainActivity.onCreate(MainActivity.java:18)

The MainActivity.java:18 Line Contain :

ArrayList<BookStore> bookStoreArrayList = HTTTP_REQUEST.readFromJson(HTTTP_REQUEST.jsonResponse);

The HTTTP_REQUEST.java:58 Line Contain :

 JSONObject listPrice = saleInfo.getJSONObject("listPrice");

Answer 1

感谢您发布 logcat 错误。这是您的项目未显示在屏幕上的原因。查看您提供的 json 数据后，您需要在处理之前对 listPrice 进行空检查，因为 saleInfo 中的某些项目没有该字段。所以代替这一行：

JSONObject listPrice = saleInfo.getJSONObject("listPrice");

做： JSONObject listPrice = saleInfo.optJSONObject("listPrice");

然后对 listPrice 进行空检查：

Double amount = null;
String currencyCode = null;

if(listPrice != null) {
    amount = listPrice.getDouble("amount");
    currencyCode = listPrice.getString("currencyCode");
}

无需再添加一个内部 try/catch。此外，您需要使用 Double class，因为有可能出现空值，并且还因为您的 Bookstore 构造函数正在传递该字段。

如果有其他字段可能不在 json 响应中，那么您还需要对这些 JSONObject 添加空值检查。

Answer 2

谢谢https://whosebug.com/users/3851567/david-velasquez 的答案。并感谢 https://whosebug.com/users/2637449/md-asaduzzaman 指出使用 opt 而不是 get 的实际错误。修复该错误后，我发现更多类似的错误没有分配值，我使用 optString、OptObject 而不是 getString、getJson 并在缺少值时分配默认值。

Here are the changes that I made in the readFromJson method to solve the error:

   public static ArrayList<BookStore> readFromJson(String jsonObject) {
    ArrayList<BookStore> currentBookStore = new ArrayList<>();
    if (TextUtils.isEmpty(jsonObject)) {
        return null;
    }
    try {
        double amount=0;
        String currencyCode = "Not Available";
        String textSnippet = "No Description Available";
        JSONObject root = new JSONObject(jsonObject);
        JSONArray items = root.getJSONArray("items");
        for (int i = 0; i < items.length(); i++) {

            JSONObject currentBook = items.getJSONObject(i);
            JSONObject volumeInfo = currentBook.getJSONObject("volumeInfo");
            String fTitle = volumeInfo.getString("title");
            String lTitle = volumeInfo.optString("subtitle");
            JSONArray author = volumeInfo.getJSONArray("authors");
            String authorName = author.getString(0);
            int PageCount = volumeInfo.getInt("pageCount");
            JSONObject saleInfo = currentBook.getJSONObject("saleInfo");

                JSONObject listPrice =saleInfo.optJSONObject("listPrice");
                if(listPrice != null) {
                    amount = listPrice.getDouble("amount");
                    currencyCode = listPrice.getString("currencyCode");
                             }
                JSONObject searchInfo = currentBook.optJSONObject("searchInfo");
                if (searchInfo!=null){
                    textSnippet = searchInfo.optString("textSnippet");
                }
            BookStore bookStore = new BookStore(fTitle, lTitle, authorName, textSnippet, PageCount, amount, currencyCode);


            currentBookStore.add(bookStore);
        }
    } catch (JSONException j) {
        Log.e("readFromJson Error", "error in reading the json response", j);
    }
    return currentBookStore;
}

带有 customArrayAdapter 的 ArrayList 仅显示 1 个列表

ArrayList with customArrayAdapter only showing 1 list

java

android

json

arraylist

android-arrayadapter